A concrete mix generally comprises, as the binder component, a hydraulic cement, e.g. portland cement, water and an aggregate component which may comprise sand and gravel granules in a suitable particle size range.
Such mixes are prepared to the desired consistency and can be applied by pouring to form concrete bodies and layers.
Frequently, however, it is desirable to utilize a spray placement method whereby a concrete deposit is formed on a substrate. Pneumatic spray techniques and air guns have been used in a wide variety of applications, for example, to repair mortar structures by driving the concrete mix into openings previously prepared to receive the mix, to coat metallic and other bodies to provide structural support or anticorrosion or antiweathering protection, for tunnel linings, for wall and ground structure stabilization and wherever the rapid placement of the mix in a dense layer is desirable.
Obviously the mix can be previously prepared and displaced by pumping to the placement gun or nozzle. The mix may have the appropriate consistency to allow it to flow and, generally speaking relatively fine aggregates, e.g. sand, may be required.
It is also known to apply the concrete composition to the substrate from a mixing nozzle in which a dry mix is combined with the requisite quantity of water to effect setting of the mixture. Such mixing nozzle guns can be used in a so-called dry-spray process.
One such technique is described in German patent document DE-OS No. 27 06 433 and, according to this publication, the binder consists either of the hydraulic cement or a synthetic resin material.
German patent document DE-OS No. 28 40 874 discloses a binder mixture or mortars which includes not only hydraulic cement but also an epoxy resin, a hardener and water.
Efforts to apply such mortars by conventional spray nozzles have, however, proved to be unsatisfactory since the nozzles were rapidly plugged presumably as a consequence of premature setting of the epoxy/hydraulic cement binder component in the presence of the water hardener or activator.
Much may also be made of the efforts described in the placement of concrete by a dry-spray process described in the journal Bauwirtschaft, issue 5, page 121 (1975). In this process, a dry mix of the aggregate and the cement is fed under pressure to a mixing nozzle and only there combined with the water.
I have extensively investigated the use of the dry spray process as described in the aforementioned journal for composition containing synthetic resin materials as part of the binder component and have discovered that significant problems arise because of the high viscosity of the resin which prevents thorough mixing with the other components, because of premature setting resulting from localized reactions of the resin with the activator or hardener and because of difficulties in feeding the resin and hardener components to the mixing nozzle when the latter is of conventional design. Furthermore, while the problem is solved by omitting, say, hydraulic cement in the system and spraying only a composition of synthetic resin, hardener and aggregate, the resulting compositions are inordinately expensive and far more expensive, for example, than cement glues or grouts. Prior intensive mixing of the resin with other components of the concrete have been attempted without successfully solving the problems.